1. Field of the Invention
The present invention relates generally to a surface modifying method of performing a surface modifying process on graphene, and more specifically to a method of adjusting the treatment temperature in vacuum to cause the surface of graphene powder to adsorb the gaseous surface modifying agent so as to modify the surface of graphene.
2. The Prior Arts
Monolayer graphite, also called graphene, is substantially an excellent material formed of a mono layer of carbon atoms, which are tightly bonded with sp2 hybrid orbital in a two-dimensional form of hexagonal honeycomb crystal. Since its thickness is only one carbon diameter about 0.335 nm and the graphitic bond is a hybrid chemical bond exhibiting the properties of a covalent bond and a metallic bond, graphene is a perfect material for electrical insulation and thermal conduction. In 2004, Andre Geim and Konstantin Novoselov at the University of Manchester in the UK successfully proved that graphene is obtained from a piece of graphite by using adhesive tape, and were thus awarded the Nobel Prize in Physics for 2010. Since then, research centers, academic organizations and related manufactures around the world have spent a great deal of resources to try to apply graphene to various industrial fields.
Specifically, graphene is the thinnest material in the world, and its electrical conductivity is higher than carbon nanotube and diamond by several times. In particular, electron mobility of graphene at normal temperature is also higher than carbon nanotube and silicon crystal, and its electrical resistivity is even lower than copper and silver. Thus, it is currently the material with lowest resistivity. Furthermore, transparent electrodes formed of graphene and carbon nanotube exhibits various advantages like high flexibility and low reflectivity, and becomes one of the best options for modern flexible electronic materials.
However, graphene has one disadvantage in actual applications. In comparison with the traditional dispersion containing carbon nanotube, the dispersion formed by dispersing graphene in some dispersion medium has poor performance in a coating process. The reason is that graphene is easy to aggregate and stack together such that its dispersion effect is very limited. It is one primary bottleneck for current industries to exploit the technology to manufacture a thin film formed of mono layer graphene which does not stack to each other and still keeps in contact for electrical connection among the graphene sheets.
To overcome the above problem, many advanced skills have been developed. Some examples will be briefly described in the following context.
In US publication No. 2010/0056819 invented by Bor Z. Jang and Aruna Zhamu, a process for producing nanographene platelets (NGPs) that are both dispersible and electrically conducting is disclosed. The process employs an oxidation treatment. High reactive oxidant gas is reacted with graphitic material, carbon material or carbon nanotube to obtain the dispersible NGP material possessing oxygen containing functional groups. However, the reaction gas in use is mostly strong corrosive, and the product formed after the oxidation treatment contains high amount of oxygen, leading to poor performance in electrical conductivity.
In addition, U.S. Pat. No. 7,745,528 taught functional graphene-rubber nanocomposites. Functionalized graphene sheets (FGS) used to form the nanocomposite is prepared by first oxidizing the graphite material to obtain oxidized graphite or separate swollen graphene sheets, and then fast heating the oxidized graphite or separate swollen graphene sheets so as to release the gas contained inside. The FGS contains oxygen rich functional groups. However, the amount of oxygen rich functional groups in the FGS has a wide variable range from 5% to 40% calculated according to the actual oxygen content. It is thus hard to precisely control the content of the functional group, and the electrical properties are not well satisfied.
From the above description for the prior arts, it is well known that all the traditional surface treatments of graphene are implemented by specific chemical reaction. Not only the process is not easily controlled, but also toxic matters are generated in the scaled up step for mass production and a crucial problem of environment protection is resulted in. Such a process is adverse for mass production of graphene in practical industrial applications.
Therefore, it greatly needs a new surface modifying method by means of physical adsorption to perform a surface modifying process on graphene without using any chemical reaction, thereby preventing the side effects generated by reactive chemicals and completely overcoming the problems in the prior arts.